U.S. patent application number 10/260252 was filed with the patent office on 2004-04-01 for aerodynamics of small airplanes.
Invention is credited to Cordy, Clifford Bernard JR..
Application Number | 20040061025 10/260252 |
Document ID | / |
Family ID | 32029645 |
Filed Date | 2004-04-01 |
United States Patent
Application |
20040061025 |
Kind Code |
A1 |
Cordy, Clifford Bernard
JR. |
April 1, 2004 |
AERODYNAMICS OF SMALL AIRPLANES
Abstract
The inventions described here provide better aerodynamics in
small airplanes. They were specifically developed to optimize
performance of a single-engine, canard airplane with the engine in
front. Some are applicable to other types of airplanes. The
specific improvements are: locating the canard so the main spar
passes in front of the engine; mounting the front of the engine
directly to the canard structure; mounting flaps on both the canard
and main wing; making the canard function as an elevon; building a
full flying canard; building the main wing with two spars and
seating the people between them; using a forward pointing steering
arm on the rudder. Each of these innovations reduces the
aerodynamic drag on the airplane in flight. This results in higher
top speed, better rate of climb, higher ceiling, and better fuel
efficiency. Some of the innovations also provide better landing
characteristics. Some also reduce total weight for even greater
performance gains, especially for rate of climb.
Inventors: |
Cordy, Clifford Bernard JR.;
(Reno, NV) |
Correspondence
Address: |
Dr. Clifford B. Cordy Jr.
6402 Mae Anne #20
Reno
NV
89523
US
|
Family ID: |
32029645 |
Appl. No.: |
10/260252 |
Filed: |
September 30, 2002 |
Current U.S.
Class: |
244/45A |
Current CPC
Class: |
B64C 1/26 20130101; B64D
27/08 20130101; B64C 3/185 20130101; B64C 39/12 20130101 |
Class at
Publication: |
244/045.00A |
International
Class: |
B64C 003/28; B64C
039/12 |
Claims
1 An airplane comprising an engine located toward a front end of
said airplane, a propeller mounted ahead of said engine, a main
wing located near a center of said airplane, a vertical stabilizer
and rudder mounted at the rear of the said airplane, and a canard
mounted to said airplane with a main structure of said canard
located in front of said engine.
2 An airplane as described in claim 1 wherein said engine is
mounted to said canard structure.
3 An airplane as described in claim 1 wherein said canard comprises
control surfaces functioning as elevons.
4 An airplane as described in claim 1 wherein said canard operates
as a full flying canard.
5 An airplane as described in claim 1 further comprising flaps
mounted on both said main wing and said canard.
6 An airplane comprising a low wing further comprising two
mechanically strong structures, said structures allowing the people
seated in said airplane to sit between said structures, positioned
below a level of a top surface of said wing.
7 An airplane comprising a rudder control mechanism with a single,
forward-pointing arm capable of moving thru its required range of
travel within the width of a fuselage of said airplane, said
fuselage being substantially as wide as the thickness of a root of
a vertical stabilizer.
Description
RELATED APPLICATIONS--NONE
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT--NONE
INNOVATIONS TO BE COVERED
[0001] A Canard
[0002] 1 Canard in front of the engine
[0003] 2 Engine mounted to canard spar
[0004] 3 Canard with elevons
[0005] 4 Full flying canard
[0006] 5 Flaps on both wing and canard
[0007] B Seating within wing having double spars
[0008] C Totally enclosed, forward pointing rudder arm
ABBREVIATIONS AND CONVERSION FACTORS
[0009] TAS--true air speed
[0010] CG--center of gravity
[0011] m/s--meters per second
[0012] km/l--kilometers per liter
[0013] 1 m/s=2.2374 mph (used for speed)
[0014] 1 m/s=196.85 ft/min (used for rate of climb)
[0015] 1 km/l=2.252 mpg (used for fuel consumption)
BACKGROUND
[0016] Canard airplanes are inherently more efficient and safer
than airplanes with a horizontal tail. The canard lifts where the
horizontal tail pushes down. Hence there is less lift induced drag
in a canard airplane. A properly loaded canard airplane cannot
stall or spin. Hence it is safer. Still, canard airplanes have
never been very popular. Existing designs have compromises that
limit their usefulness. The major compromises include a severely
limited range of position for the center of gravity (CG) and high
takeoff and landing speeds.
[0017] In the last couple decades, experimental aircraft builders
have made significant improvements in the performance of small
planes. Some of these deserve mention here because some of the
innovations described in this application are extensions to their
work. First, the major proponent of canard aircraft is Burt Rutan.
His best known planes are the VARI-EZE (which spawned a whole
family of canard aircraft) and the Voyager (which flew around the
world without refueling). A good quality VARI-EZE typically reaches
a top speed of 90 m/s. Second, the most popular homebuilt planes in
the world are the RV family, designed by Dick Van Grunsven. These
are conventional airplanes with horizontal tails. A good quality RV
typically reaches a top speed of 90 m/s. Both these designs fly
about twice as fast as a small Cessna (for example) using little,
if any, more power. Thus they go about twice as far on any given
amount of fuel.
[0018] Klaus Savier, Santa Paula, Calif., built the world's fastest
VARI-EZE. He increased the power produced by the standard engine by
about 30% (which should give a 9% speed increase to about 98 m/s)
and has streamlined a VARI-EZE to reach top speeds of about 110 m/s
and fuel economy of 21 km/l at 90 m/s. Dave Anders, Visalia,
Calif., built the world's fastest RV-4. He boosted the power by 50%
(which should give a 15% speed increase to 103 m/s) and has
streamlined it to reach a speed of 122 m/s. The work of both these
builders is well known within the experimental aircraft
community.
[0019] Another airplane that deserves mention is the AR-5, which
was designed from scratch by Mike Arnold. It is a conventional
style airplane with outstanding aerodynamics. It is a one place
airplane powered by an engine producing 45 kW. It flew 93 m/s in
level flight and set a world record of 95 m/s for airplanes
weighing under 300 kg in flight. (The official race rules allow
some descent over the measured distance.) There are no plans or
detailed information about this airplane. It has been studied
carefully only by a few specialists at the invitation of the
owner/builder. One known problem in the airplane is that the engine
overheats with little provocation. Marginal cooling is one solution
to the cooling drag problem. This might be acceptable for a single
purpose airplane designed to break a speed record, but it is not
acceptable in a general purpose aircraft.
[0020] One big disadvantage of the EZ family is the limited range
of CG with which it can be flown safely. This results in the
condition that, on the ground, the plane falls over backward when
the pilot is not in it. The EZ airplanes are tricycle gear planes
with the engine in the rear. If it falls over backward, it
generally causes serious damage. The main disadvantage of the RV
family is that they are conventional airplanes, hence can stall and
spin if the speed is not high enough. Neither family of airplanes
is designed to be as aerodynamic as desirable and the exceptional
performance achieved by Klaus and Dave are the result of
considerable investment of personal time and ingenuity.
[0021] There is no prior single engine canard airplane that has a
reasonably wide range of allowable CG position. The main difficulty
in designing a single engine canard airplane is that the engine
must be at the front or rear of the airplane, not on the wing, as
is possible in a twin engine airplane. Placing the engine above the
airplane is theoretically possible, but that introduces a whole set
of undesirable mechanical and aerodynamic problems. In existing
airplanes with the engine in front, as in the Quickie family, the
canard has to carry the majority of the weight of the airplane.
This forces the canard to be large, and it almost becomes the wing.
To keep the wing far enough forward to function as a wing instead
of a horizontal stabilizer, the distance from the wing to the
canard must be small. This results in an undesirably critical
location of the CG. If the engine is in the rear, as in the EZ
family, and in the original incarnation of the race airplane named
Pushy Galore, the wing carries most of the weight, but the pusher
configuration introduces a new set of limitations, including the
impossibility of making a taildragger configuration (with a small
tail wheel as opposed to a nose wheel) and less efficient engine
cooling.
[0022] No existing canard airplane that is designed to fly fast
provides the ability to fly and land at low speeds. In conventional
aircraft, slow flight is achieved by using wing flaps. In a canard
design, the use of wing flaps would actually increase the minimum
flying speed.
SUMMARY
[0023] This invention consists of several improvements to the
aerodynamics of small airplanes. While the impetus for these
innovations is improving the performance of canard aircraft with
front engines, several of the novel designs are also applicable to
conventional aircraft with horizontal tails and also to pusher
aircraft. The specific improvements presented here are: The canard
is located in front of the engine to give a wider range of
acceptable CG locations. The engine is mounted directly to the
canard structure. The control surfaces on the canard are elevons,
eliminating the need for control surfaces on the wing. A "full
flying" canard is used to achieve more control authority from the
control surfaces. Flaps are mounted on both the wing and canard to
give the ability to fly slower without increasing the size of the
wing and canard (which would increase drag). The wing contains two
spars, allowing the pilot and passenger to sit in the wing, rather
than on it, reducing the frontal and surface areas of the fuselage.
The rudder control mechanism is much narrower, allowing it to be
completely enclosed within a fuselage of normal width, thus
eliminating aerodynamic drag.
BRIEF DESCRIPTION OF THE ILLUSTRATIONS
[0024] FIG. 1 is a top view of the front of the airplane showing
the location of the canard with its spar located in front of the
engine.
[0025] FIG. 2 is a side view of a section of the airplane cabin
showing the seat located within the wing, between the two main wing
spars.
[0026] FIG. 3 is a top view of a standard rudder steering
assembly.
[0027] FIG. 4 is an isometric view of a much narrower rudder
steering assembly.
[0028] FIG. 5 is a top view of the new, narrow rudder steering
assembly with the rudder at the maximum right turn position.
DETAILED DESCRIPTION OF THIS INVENTION
[0029] Canard Location
[0030] The secret of success in designing a canard airplane with a
single engine in front is to get the canard far enough forward that
it does not carry too much weight. In the Quickie family, the
canard is located just below and behind the engine. If everything
is balanced just right, this is not a terrible situation,
especially at high speed. But the big canard, heavily loaded, and
big elevators, generate excess lift induced drag and control
surface drag, especially at lower speeds such as at takeoff,
landing, and during maximum climb. The lift induced drag also
increases with altitude, limiting the altitude that the plane can
reach, and limiting its speed at altitudes it can reach. It would
be desirable to move the canard forward and place the engine in the
center of the canard. Structurally, this is impractical. It would
be very difficult to build a structure that maintains the required
strength of the canard and still allows the required access to the
engine. Placing the canard under the engine would compromise the
aerodynamics of the airframe. Placing the canard over the engine
would not only compromise the aerodynamics, it would also interfere
with the view of the pilot.
[0031] This novel design places the canard somewhat in front of the
engine. This has never been done before. The main disadvantage is
that a long prop extension is required to give sufficient clearance
between the propeller and the canard. There are many advantages.
This far-forward canard carries a smaller fraction of the total
weight, giving aerodynamic advantages in the lift induced drag and
control surface drag (relative to a Quickie, for instance). The CG
has a much wider range of acceptable locations. The front of the
engine can be mounted directly to the canard (which basically is
carrying the engine in any case) rather than having those forces
transmitted thru the airframe. Of course, adequate structure must
be provided to keep the canard attached to the rest of the
airplane. Depending on the design details, this will generally be
simpler and lighter than the structure required for a bed mounted
engine. If the airplane is tricycle gear, the nose wheel can be
mounted to the canard structure also. The nose wheel carries much
of the engine weight on the ground, relieving stress on the
fuselage structure caused by a hard landing.
[0032] The best, though not the only, implementation of this
arrangement is shown in FIG. 1. The canard (1) with elevator (2)
has a spar (3) that passes just in front of the engine (4) and just
below the propeller shaft (5). The spar should be located as far
forward as practical within the canard. This locates the canard as
far back as possible, in order to minimize the length of the prop
extension (6). Furthermore, the location off the spar (3) is such
that it is easy to connect the front engine mounts (7) to it.
[0033] This innovation, placing the canard in front of the engine,
gives greater tolerance to CG location, reduces stresses in the air
frame, and improves aerodynamics.
[0034] Canard with Elevons
[0035] Elevons (a combination of elevator and aileron in a single
control surface) are a well known but seldom used control
configuration. The elevon is mechanically the same as an elevator
except the linkage is such that the two control surfaces can be
moved in opposite directions to produce a roll moment. The aileron
is eliminated entirely, producing a simpler, lighter,
aerodynamically cleaner wing. The usual limitation of an elevon
design is that there is insufficient roll control. A few
conventional aircraft do use elevons. Elevons were tried on some
very early VARI-EZEs, but with their very small canard, there was
not enough roll control. In a design with a larger canard, as in
the Quickie family, canard elevons would probably work, but they
were never tried. With a reasonable size canard located in front of
the engine, using elevons for roll control should be a satisfactory
configuration.
[0036] This innovation, using elevons on a canard airplane with the
engine in front, eliminates the need for an aileron, and results in
a simpler, lighter, more aerodynamic wing.
[0037] Full Flying Canard
[0038] A canard (or horizontal tail) usually has some fraction of
the surface hinged for the elevator function. The entire canard (or
horizontal tail) could be rotated as an elevator. This is rarely
done. The problem is that the angle of attack becomes too large and
the surface stalls before there is enough response to the elevator
function. A "full flying tail" is a structure where the entire
horizontal tail rotates a small amount and the elevator part of the
tail rotates considerably more. The linkage that accomplishes this
is well known and very simple. This gives very good elevator
response. This new innovation extends the concept of a full flying
tail to the canard and creates a full flying canard. The control
linkages are the same as in the full flying tail.
[0039] With the control power of a full flying canard, elevons
become practical on a small canard. This is an additional
innovation, which is also applicable in the horizontal tail. There
has never been a full flying canard. There has never been a full
flying tail used as an elevon. There certainly has never been a
full flying canard used as an elevon.
[0040] These innovations, the full flying canard and the full
flying elevon, give improved roll authority to the canard and
elevon, eliminating the need for an aileron, and making a simpler,
lighter, more aerodynamic wing.
[0041] Canard Flaps
[0042] Most canard airplanes do not have flaps. The reason is
simple. In a canard airplane, wing flaps are counterproductive. A
flap does three things. It increases the maximum coefficient of
lift. It decreases the angle of attack for any given coefficient of
lift. It also moves the center of lift aft. A wing flap, moving the
center of lift aft, increases the load on the canard, and increases
the minimum achievable flying speed. Since canard airplanes do not
have flaps, their landing speeds are typically 20% to 30% higher
than conventional aircraft with similar wing loading. This is
undesirable. A canard flap alone is unacceptable because the
lifting capacity of the canard could be increased to the point that
the wing might stall, with likely fatal consequences.
[0043] A novel solution to the high landing speed problem is to put
flaps on both the wing and canard with the linkage coordinated so
the canard flaps cannot be used without the wing flaps. In this
configuration, the maximum coefficients of lift of both flying
surfaces are increased by similar amounts, yielding lower flight
(and landing) speeds. Ideally, the flaps on the canard would be
made slightly more powerful than the wing flaps. This would
compensate for the aft movement of the center of lift as the flaps
are deployed.
[0044] Wing flaps provide an additional factor of safety. If the
pilot manages to load the airplane with the CG aft of the
acceptable range, and then flies too slowly, the wing and canard
can get into a condition where neither of them can support their
load, and there is enough flow separation that the elevators lose
their effect. The plane descends rapidly, although it does not
plummet, and the landing will likely break the airplane, even if it
is on a smooth, level surface. This condition has occurred in the
Quickie II. In this condition, deploying only the wing flaps
slightly (into the non-separated air flow below the wing), but not
the canard flaps, will increase the lift of the wing, move the
center of lift aft, cause the plane to rotate nose down, pick up
speed, and recover from the impending stall condition.
[0045] The wing flaps can be the same as are found on most
conventional aircraft. The canard flaps could be something as
simple as having the elevator motion accommodate a larger than
usual range of downward motion. The elevator motion is limited by a
linkage to the wing flap control to prevent the elevator from
extending too far down unless the wing flap is extended. The canard
flaps could also be made larger than the elevator and be controlled
directly by the flap control mechanism. There is nothing
necessarily unique in the mechanisms that drive the flaps and
elevators. The unique innovation is the use of flaps on the
canard.
[0046] This innovation, providing flaps on both the wing and
canard, and having them linked so the canard flaps cannot be
deployed without deploying the wing flaps, allows lower flight and
landing speeds. It also improves safety margin by providing a means
for recovery from an impending stall where the elevator has lost
its ability to pull the nose down.
[0047] Wing Structure
[0048] In a single-place airplane, or a two-place, side-by-side
airplane, with the canard in front of the engine, the people will
sit at approximately the center of the chord of the wing. For
minimum air drag, the frontal (and total surface) area of the
fuselage should be minimized. This is best done by having the
people sit on the floor of the airplane in a recumbent position. In
this position, the people and the wing must occupy the same volume
of space. This could be uncomfortable. In the past the solution has
been to yield on the desire for minimal areas and have the people
sit on top of the wing, as in the AR-5. Several other airplanes are
designed so the people sit below the level of the top of the wing,
but far enough aft with respect to the wing that the wing spar (or
equivalent structure) passes under their knees. Having the seats
within the wing structure (instead of behind it) keeps the people
closer to the desired CG of the airplane. Thus there is less effect
on balance from the number, or size, of people in the airplane.
[0049] A novel solution to the problem is to have the people sit in
the wing, as shown in FIG. 2. This is achieved by building the wing
(1) with two spars (2 and 3) (or equivalent structure), instead of
the usual one spar. The front spar (2) passes thru the fuselage
under the thighs of the people, the rear one (3) passes thru the
fuselage under their lower back. The seat (4) is shaped so the
people do not feel like they are sitting on two railroad rails. The
top surface of the wing (5) is interrupted where it passes thru the
cockpit, the loss of strength being made up by bands of fiber (6)
near the tops of the spars (2 and 3).
[0050] This innovation, using a wing with two spars and seating the
people within the wing structure, minimizes the frontal and surface
areas of the fuselage, thus reducing aerodynamic drag and improving
performance.
[0051] Totally Enclosed Rudder Control
[0052] In most small airplanes, the rudder pedals control a pair of
cables connected to an inverted T-shaped structure at the base of
the rudder, with the arms of the T extending sideways from the
rudder shaft. This is shown in FIG. 3. The rudder cables (3) are
connected to the steering arms (1) at a flexible joint (2). It is
hard to beat this configuration for simplicity and reliability.
However, the steering arms (1), the ends of the cables (3), and the
connection between the two (2) are usually located in the high
speed air flow passing over the airplane, and they are generally
high drag components. Sometimes they are enclosed in protrusions
from the sides of the fuselage to reduce aerodynamic drag.
Typically the lever arm for the rudder cable attachment (2) is 50
mm. To enclose this assembly within the skin of the airplane (4)
would require the fuselage to be a minimum of 120 mm wide at the
position of the rudder shaft. This would increase the total surface
area of the airplane so much that it has more drag than the
external rudder cable assembly. Building a protrusion to house the
steering arms does improve aerodynamics somewhat, but it is not a
clean solution.
[0053] The aft end of the fuselage (not including the tail) is
typically more or less conical with an apical half angle of about
10.degree.. This is shown in FIGS. 3 and 5.
[0054] The innovation presented here is a simple mechanism that is
much narrower than existing steering mechanisms. This allows the
entire steering mechanism to be contained within the fuselage,
eliminating air drag and maximizing speed and efficiency. The new
mechanism is shown in FIG. 4 and FIG. 5. FIG. 4 is an isometric
view with the rudder pointed straight back, and the steering arm
pointed straight forward. FIG. 5 is a top view with the rudder
25.degree. to the right, typically the maximum desired movement.
The rudder shaft (1) is connected to a forward pointing steering
arm (2). Rudder cable (3) follows a path above the rudder arm (2).
Rudder cable (3) is anchored to the rudder arm (2) at a termination
(5) that need not be flexible. From there it passes around the
fixed turning post (7) which is mounted on the rudder arm (2) and
around the pulley wheel (9) which is mounted to the fuselage. The
other rudder cable (4) follows a mirror image path below the rudder
arm (2). Rudder cable (4) is anchored to the rudder arm (2) at a
termination (6) that need not be flexible. From there it passes
around the fixed turning post (8) which is mounted to the rudder
arm (2) and around the pulley wheel (10) which is mounted to the
fuselage. This entire assembly, except for the forward pointing
rudder arm (2) and turning posts (7 and 8) can be built with
standard aircraft parts. As can be seen in FIG. 5, this rudder
steering mechanism can be entirely housed between the walls of the
fuselage (11 and 12) with very little more total width at the
rudder shaft (1) than the lever arm of the steering cables (3 and
4), typically 50 mm. This is only 40% of the width required by the
conventional steering gear. For reasons of structural strength and
rigidity, it is generally undesirable to make the aft end of the
fuselage that narrow. Thus, the width of the aft tip of the
fuselage is no longer limited by the steering mechanism.
[0055] In theory, a simpler assembly could be built if the rudder
control cables were magically attached to the front of the
forward-pointing rudder control arm. Unfortunately, magic is not
reliable enough for aircraft applications, and existing, approved
hardware for terminating cables are the sizes shown in FIGS. 4 and
5.
[0056] The novel parts of this design are the use of guide wheels
(9 and 10) and turning posts (7 and 8) to connect the rudder cables
(3 and 4) to a forward pointing arm (2) which can rotate thru its
required range of motion totally within the skin of the fuselage.
This eliminates air drag associated with the rudder control
mechanism
* * * * *